Polymeric compounds having CO groups in the backbone chain have been known in the art and typical examples are polyketones produced by copolymerization of ethylene and carbon monoxide. The synthesis of such polyketones is fairly old and was first discovered by F. Ballauf et al. in 1941 (German Pat. No. 863,711). Since then, many improvements have been proposed.
A variety of polymeric compounds retaining a number of carboxyl groups in the molecule, such as polyacrylic acid and copolymers of maleic acid with other olefinic compounds have been extensively used as polyelectrolytes for many years. A number of resins capable of high water absorption have also been proposed; they include the products of crosslinking of sodium polyacrylate with chlorohydrin, 1,3-dichloroisopropanol, glycidyl ether, etc. (Japanese Laid-Open Patent Application No. 82143/75); the product of crosslinking with polyvalent metal ions (Japanese Laid-Open Patent Application No. 112787/76); and copolymers of vinyl acetate and acrylic acid salts.
Polyelectrolytes intended for use as builders in detergents have also been proposed and they include: polyacrylic acid salts (Japanese Laid-Open Patent Application No. 43707/72); the copolymer of maleic anhydride and ethylene (U.S. Pat. No. 3,764,586); and the copolymers of maleic anhydride and long-chain alkylenes (Japanese Laid-Open Patent Application No. 12807/73).
However, the so far proposed polyelectrolytes do not have high environmental degradability and because of their potential hazard of pollutions due to residual products, the use of such polyelectrolytes has been limited.
Attempts have been made to introduce CO groups in the backbone chain of conventional polyelectrolytes and an approach based on copolymerizing maleic anhydride with carbon monoxide is described in U.S. Pat. No. 3,764,586. However, the experiments conducted by the present inventors have revealed that the yield of the copolymer produced by this method is too low to warrant its commercial use.
The present invention offers a solution to these problems of the prior art by providing a novel terpolymer having CO groups in the backbone chain. The novel terpolymer of the present invention can be used as a highly water-absorbing resin, a detergent builder, etc. which exhibit improved performance and can be discarded after use without any potential risk of environmental pollution. Therefore, the advent of the novel terpolymer of the present invention will contribute to expansion of the area where polyelectrolytes can be employed with advantage. In particular, the terpolymer will find great commercial value as a detergent builder since its performance is comparable to that of condensed phosphates such as sodium tripolyphosphate (STPP) and because it is advantageous over the latter in terms of reduced eutrophication, improved biodegradability and increased safety to humans.
Because of their high performance and low cost, STPP have been used most commonly as builders in detersive systems. However, with the concern over eutrophication of rivers and lakes due to the increased content of phosphorus compounds in surface water, shifting to builders other than condensed phosphate compounds has recently been undertaken at a rapid pace. For example, zeolites which are inorganic compounds that have no potential problems with eutrophication or human toxicity have been proposed as substitutes for condensed phosphate compounds. However, being water-insoluble solids, zeolites are not completely satisfactory in performance and the detergency of systems incorporating zeolites as builders is inferior to that of systems employing STPP. Furthermore, zeolites cannot be incorporated in liquid detersive systems. Under these circumstances, compounds having the ability to sequester metal ions comparable to that of STPP have been reviewed and the polyelectrolytes so far developed to meet this need include polyvalent carboxylic acids such as citric acid and succinic acid, N-containing carboxylic acids such as nitrilotriacetic acid, polyacrylic acid, as well as the aforementioned copolymer of maleic anhydride and ethylene (U.S. Pat. No. 3,764,586) and copolymers of maleic anhydride and long-chain alkylenes (Japanese Laid-Open Patent Application No. 12807/73).